Biomedical subjects

K Seuwen

Publications and source records attributed to K Seuwen.

41 records · Page 3Linked to original sources

PubMed1984

Cellular content of ribosomal RNA in relation to the progression and competence signals governing proliferation of 3T3 and SV40-3T3 cells.

The method for differential fluorescence staining of cellular RNA and DNA by acridine orange (AO) was optimized for 3T3 and SV40-3T3 cells. Cellular contents of DNA and of ribosomal RNA (rRNA) were determined by dual-channel flow cytometry during cell-density-dependent proliferation and after stimulation of quiescent cells. With increasing density of 3T3 cells, cellular content of rRNA decreases by about 60%, whereas SV40-3T3 cells do not exhibit a significant dependence of rRNA content on cell density. 3T3 cells stimulated early after becoming quiescent resume reaccumulation of rRNA after a delay of only 4 h, whereas cells maintained at quiescence for several days exhibit a delay of about 12 h before a significant rise of rRNA is observed. The extent of rise of cellular rRNA content after different regimens of stimulation of quiescent 3T3 cells does not correlate well with the fraction of cells entering the cell cycle. These and other reported instances of discordance between rRNA content and stimulation into the cell cycle are resolved by showing that of the two signals governing entry into the cell cycle only the progression signal, but not the competence signal is associated with reaccumulation of cellular rRNA. The present results are consistent with the progression function being in essence the achievement of a threshold number of ribosomes per cell, which in conjunction with the competence signal is sufficient for initiation of the cell cycle.

Animals↗

PubMed1983

Only one of the two signals required for initiation of the cell cycle is associated with cellular accumulation of ribosomal RNA.

Two intracellular functions are elicited by the serum component in culture media in order to initiate the cell cycle: "competence" and "progression". Although both functions have to be present simultaneously for start of cell division, it is shown here for Swiss 3T3 cells that only one of them, the progression signal, is associated with reaccumulation of ribosomal RNA. This result points to the cellular complement of ribosomes as one of the limiting parameters for cell division.

Animals↗

PubMed1983

Proliferative activity and ribosomal RNA content of 3T3 and SV40-3T3 cells.

The phenomenon of resistance of confluent 3T3 cells to serum stimulation of proliferation is investigated and shown to depend drastically on the kinetics of application of growth factors with the serum. The cellular content of ribosomal RNA is determined flow-cytometrically by measuring the red fluorescence of cells stained with acridine orange. Ribosomal RNA content of 3T3 cells, but not of SV40-3T3 cells, is shown to decrease after confluence. The kinetics of restoration of ribosomal RNA in stimulated 3T3 cells exhibits an increasing delay with increasing duration of quiescence. These and further results are consistent with "progression" to initiation of the cell cycle being closely associated with restoration of cellular content of ribosomes.

Animals↗

PubMedDate not supplied

A novel calcium sensor stimulating inositol phosphate formation and [Ca2+]i signaling expressed by GCT23 osteoclast-like cells.

Osteoclast activity is inhibited by elevated [Ca2+]o; however, the underlying molecular mechanism is unknown. We used the human osteoclast-like cells GCT23 to elucidate their cation-sensing properties. Cells responded to elevated [Ca2+]o with rapid concentration-dependent [Ca2+]i transients (EC50 = 7.8 mm, time to peak 44 +/- 4 sec) that were due to release from intracellular stores, followed by Ca2+ influx across the plasma membrane. Ca2+ store depletion by thapsigargin, endothelin-1, or bradykinin activated calcium entry pathways. Cells responded similarly to Ni2+ and Cd2+ with albeit slower kinetics (EC50 <10 microm and <100 microm, times to peak 140 +/- 25 sec and 150 +/- 24 sec, respectively). The three cations stimulated inositol phosphate production (two-fold, p <.02) similar to bradykinin (2.5-fold, p <. 002), which activates a phospholipase C (PLC)-coupled receptor in GCT23 cells. The cells did not respond to 0.1-1 mM Gd3+ or neomycin B, indicating that the parathyroid calcium receptor (PCaR) is not functionally expressed. In confirmation, PCaR could not be detected by reverse transcriptase polymerase chain reaction in GCT23 cells and in mouse osteoclasts, and the calcimimetic compound NPS R-568 failed to produce the left shift of the concentration-response curve characteristic for PCaR. Our data demonstrate for the first time that cation sensing by osteoclast-like GCT23 cells is mediated by a PLC-coupled receptor that is not identical to PCaR.

Animals↗

PubMedDate not supplied

The specificity of ionophore A23187 in cation transport across lipid membranes. Studies with lecithin vesicles.

Lecithin vesicles containing different cations were prepared by sonication and characterized. When the concentration of the divalent cations in the buffer was increased from 1 mM to about 100 mM the cation-concentration inside of the vesicles did not increase proportional to the outside concentration, but showed a saturation behaviour. The efflux of various cations mediated by ionophore A23187 was measured and relative transport-rates were determined. The following sequence was obtained: Zn2+ > Ca2+ > Mg2+ > Sr2+ > Ba2+ approximately Li+ > Na+. The efflux of Ca2+ increased proportional to the square of the A23187-concentration. To lecithin-vesicles containing ethylenediamine tetraacetate (EDTA) inside different cations were added on the outside. In the presence of A23187 divalent cations are transported into the vesicles and bound there by EDTA. During the influx of Me2+-ions into vesicles a H+-efflux was observed. The resulting pH-decrease was measured. The rate of the pH-change depended on the Me2+-ion used. The sequence was: Cd2+ > Zn2+ > Ca2+ > Mn2+ > MG2+ > Sr2+, Ba2+.

Anti-Bacterial Agents↗